The present invention relates to plate boehmite, plate alumina and their manufacturing methods.
Boehmite and alumina are useful, for example, heat-resistant materials such as flame-retarding fillers for plastics, carriers for high-temperature catalysts, high-temperature-resistant lubricants and refractory; moisture sensors, solid electrolytes, various kinds of electronic devices, separating membranes, fluorescent materials, lubricants and coating materials. Particularly, xcex2-alumina has found wide application for or as moisture sensors, solid electrolytes, various kinds of electronic devices, separating membranes and fluorescent materials.
Recently, gas turbine power generation resorting to high-temperature combustion is becoming the norm in the field of power generation, and the combustion temperature tends to be increasing for purposes of energy efficiency. Accordingly, high temperature catalyst carriers with high performance are in demand. Further, there is an increasing demand for solid electrolytes for sodium-sulfur (NaS) type batteries directed to storage of surplus power and gas separating membranes for effective use of various kinds of gases, and the demand for alumina materials is on the increase.
However, conventional alumina materials involve various problems. While alumina materials having various types of crystal forms have been used as combustion catalyst carriers, particulate alumina, which is used as alumina combustion catalyst carrier, has a relatively small specific surface area of less than 10 m2/g. Accordingly, the alumina particles show low catalytic activity. Meanwhile, combustion in a gas turbine is carried out in a high-temperature range, for example 1200 to 1400xc2x0 C. Thus, if alumina is used as a catalyst carrier, the alumina particles are caused to undergo sintering or growth by the heat of combustion in the gas turbine. As a result, the specific surface area of the alumina particles is reduced further, which makes them ineffective as a catalyst.
It is well known that alumina has various modifications.
xcex1-Alumina is most thermally stable among other modifications and can be manufactured relatively easily. However, xcex1-alumina is a so-called corundum, so that it has a small surface area. Accordingly, xcex1-alumina shows low catalytic function. xcex8-Alumina and xcex4-alumina, which are plate crystal forms, have relatively large surface areas, so they have high catalytic activity. However, xcex8-alumina and xcex4-alumina undergo a phase transition in high temperature conditions of 1150xc2x0 C. or higher. Under such conditions, the surface areas of these alumina decrease suddenly, and the physical properties thereof are altered greatly. In the case of xcex2-alumina containing sodium, the sodium undergoes transpiration in high temperature conditions. The transpirated sodium damages heating equipment. In addition, xcex2-alumina cannot be manufactured easily.
The above-described shortcomings and drawbacks with respect to alumina apply also to boehmite, which is a raw material of alumina.
A first objective of the present invention is to provide a plate boehmite, which has a large specific surface area and high catalytic activity, and a method of manufacturing the plate boehmite.
A second objective of the present invention is to provide a plate alumina, which has a large specific surface area, high catalytic activity and high heat resistance, and a method for manufacturing the plate alumina.
In order to attain the above objectives, a method for manufacturing a plate boehmite is provided in a first aspect of the present invention. In this manufacturing method, raw materials including a compound containing at least one kind of alkaline earth metal selected from calcium, strontium and barium (alkaline earth metal compound); aluminum hydroxide; and water are pressurized and heated at a temperature of 150 to 300xc2x0 C. The raw materials, after having undergone this pressurizing and heating step, yield a reaction product. Subsequently, the surplus alkaline earth metal compound remaining in the reaction product is removed.
A method for manufacturing a plate alumina is provided in a second aspect of the present invention. According to this manufacturing method, raw materials including a compound containing at least one kind of alkaline earth metal, which is selected from calcium, strontium and barium (alkaline earth metal compound), and aluminum hydroxide are pressurized and heated at a temperature of 150 to 300xc2x0 C. in the presence of water. The raw materials, after having undergone this pressurizing and heating step, yield a plate boehmite. Subsequently, the surplus alkaline earth metal compound remaining in the plate boehmite is removed, followed by calcination of the plate boehmite at a temperature of 450 to 1500xc2x0 C.
A plate boehmite having a plurality of layers is provided in a third embodiment of the present invention. This boehmite has an aspect ratio of from 10 to 35 and has at least one kind of alkaline earth metal selected from calcium, strontium and barium intercalated therein.
Features of the present invention thought to be novel will be made apparent particularly in the appended claims. The present invention as well as its object and advantages will be understood from the description of embodiments, which are preferred at present, with reference to the accompanying drawings.